1. Field of the Invention
The present invention relates to a photoelectric conversion device, and more particularly, it relates to a photoelectric conversion device employing a non-single-crystalline semiconductor such as a microcrystalline or polycrystalline semiconductor containing a large number of crystal grains as a photoelectric conversion layer.
2. Description of the Background Art
A photoelectric conversion device employing a microcrystalline silicon (μc-Si) semiconductor as a photoelectric conversion layer has recently been proposed in Japanese Patent Laying-Open No. 2001-284619 or 2002-76396. The term “microcrystalline silicon (μc-Si) semiconductor” denotes a semiconductor containing a large number of crystal grains having the maximum grain size of not more than about 100 nm while containing Si as the element, including that having an amorphous phase therein. The photoelectric conversion device employing microcrystalline silicon (μc-Si) as the photoelectric conversion layer is by far smaller in photo-deterioration as compared with a photoelectric conversion device consisting of amorphous silicon (a-Si).
FIG. 6 is a sectional view for illustrating the structure of a conventional photoelectric conversion device employing microcrystalline silicon (μc-Si) as a photoelectric conversion layer. The structure of the conventional photoelectric conversion device employing microcrystalline silicon (μc-Si) as a photoelectric conversion layer is now described with reference to FIG. 6.
In the conventional photoelectric conversion device, a metal electrode layer 102 of Ag having a thickness of about 300 nm is formed on the upper surface of a glass substrate 101, as shown in FIG. 6. A transparent electrode 103 of aluminum-doped zinc oxide (AZO) having a thickness of about 100 nm is formed on the upper surface of the metal electrode layer 102. A power generation unit obtained by successively stacking an n layer 104 (thickness: about 50 nm) consisting of microcrystalline silicon (μc-Si) doped with phosphorus, an i layer 105 (thickness: about 2 μm) consisting of microcrystalline silicon (μc-Si) substantially doped with no impurity for deciding the conductivity type and a p layer 106 (thickness: about 10 nm) consisting of microcrystalline silicon (μc-Si) doped with boron is formed on the upper surface of the transparent electrode 103. A transparent electrode 107 having a thickness of about 80 nm is formed on the power generation unit. A collector electrode 108 of silver paste are formed on prescribed portions of the upper surface of the transparent electrode 107. Thus constituted is the conventional photoelectric conversion device employing microcrystalline silicon (μc-Si) as a photoelectric conversion layer (the power generation unit).
FIG. 7 is a schematic sectional view for illustrating the states of crystal grains contained in the layers of the conventional photoelectric conversion device shown in FIG. 6. Referring to FIG. 7, many of crystal grains 105a contained in the i layer 105 have major axes substantially perpendicular to the main surface 101a of the substrate 101. Further, many of crystal grains 104a and 106a contained in the n layer 104 and the p layer 106 respectively have substantially isotropic shapes or major axes substantially perpendicular to the main surface 101a of the substrate 101. Thus, many of the crystal grains 104a, 105a and 106a contained in the n layer 104, the i layer 105 and the p layer 106 constituting the power generation unit are unidirectionally oriented substantially perpendicularly to the main surface 101a of the substrate 101. Further, many of crystal grains 103a contained in the transparent electrode 103 provided under the n layer 104 also have major axes substantially perpendicular to the main surface 101a of the substrate 101.
In the aforementioned conventional photoelectric conversion device employing microcrystalline silicon (μc-Si) as the photoelectric conversion layer (the power generation unit), however, the open-circuit voltage, which is an important output parameter thereof, is disadvantageously low.